Display panel and display panel manufacturing method

ABSTRACT

A display panel in which pixels each include light-emitting parts are two-dimensionally arranged across a main surface of a substrate. The light-emitting parts each include: a first electrode that is light-reflective; a first functional layer disposed above the first electrode; a light-emitting layer disposed above the first functional layer; a second functional layer disposed above the light-emitting layer and including ytterbium; and a second electrode disposed above the second functional layer and being light-transmissive. At least one of the light-emitting layer and the first functional layer is an applied film. With respect to each pixel, at least one of the light-emitting parts differs from any other of the light-emitting parts in terms of light emission color, and the at least one light-emitting part differs from the any other of the light-emitting parts in terms of film thickness of at least one of the light-emitting layer and the first functional layer.

This application claims priority to Japanese Patent Application No.2019-167004, filed Sep. 13, 2019, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a display panel in which pixelsincluding light-emitting elements such as organic electric-fieldlight-emitting elements (referred to hereinafter as organic EL elements)are two-dimensionally arranged across a main surface of a substrate, andto a method of manufacturing the display panel.

Description of Related Art

As self-luminous display panels, organic EL display panels in whichorganic EL elements are arranged in a matrix on a substrate have beenrecently put to practical use as displays of electrical equipment. Theorganic EL elements each have a basic structure in which an organiclight-emitting layer including an organic light-emitting material isdisposed between an electrode pair of an anode and a cathode. Whendriven, a voltage is applied across the electrode pair (the anode andthe cathode), and holes injected to the organic light-emitting layerfrom the anode and electrons injected to the organic light-emittinglayer from the cathode recombine to emit light. Thus, the organic ELelements are current-driven light-emitting elements.

In full-color organic EL display panels, each organic EL element havingthe above structure forms a red (R), blue (B), or green (G) subpixel andadjacent R, G, and B subpixels combine to form one pixel. Many of suchfull-color organic EL display panels adopt a so-called optical cavitystructure in order to further improve a luminous efficiency in eachlight emission color (for example, International Publication No.WO2015/194189).

According to the optical cavity structure, a film thickness of anorganic layer which is appropriate for increasing the luminousefficiency of the organic EL element of each light emission colordepends on wavelength of the light emission color. As the wavelength ofthe light emission color increases, the film thickness of the organiclayers increases. Further, organic layers having different filmthicknesses are formed by a wet process such as a printing method,mainly from the viewpoint of manufacturing costs.

Also, an electron injection transport layer is formed by doping anorganic material having electron transport properties with Ba having alow work function, thereby improving the electron injection propertiesand lowering a driving voltage.

SUMMARY

A display panel pertaining to at least one aspect of the presentdisclosure is a display panel in which pixels each includinglight-emitting parts are two-dimensionally arranged across a mainsurface of a substrate. The light-emitting parts each include: a firstelectrode that is light-reflective; a first functional layer that isdisposed above the first electrode; a light-emitting layer that isdisposed above the first functional layer; a second functional layerthat is disposed above the light-emitting layer and includes ytterbium;and a second electrode that is disposed above the second functionallayer and is light-transmissive. At least one of the light-emittinglayer and the first functional layer is an applied film. With respect toeach of the pixels, at least one of the light-emitting parts differsfrom any other of the light-emitting parts in terms of light emissioncolor, and the at least one light-emitting part differs from the anyother of the light-emitting parts in terms of film thickness of at leastone of the light-emitting layer and the first functional layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Objects, advantages, and features of the technology pertaining to thepresent disclosure will become apparent from the following descriptionthereof taken in conjunction with the accompanying drawings, whichillustrate at least one embodiment of the technology pertaining to thepresent disclosure.

FIG. 1 is a block diagram illustrating the overall structure of anorganic EL display device pertaining to at least one embodiment of thepresent disclosure.

FIG. 2 is a schematic enlarged plan view illustrating part of an imagedisplay surface of an organic EL display panel of the organic EL displaydevice pertaining to at least one embodiment of the present disclosure.

FIG. 3 is a perspective diagram illustrating a substrate after formingof banks (column banks) and pixel partition layers (row banks)pertaining to at least one embodiment of the present disclosure.

FIG. 4 is a schematic cross-section diagram, taken along a line A-A inFIG. 2, pertaining to at least one embodiment of the present disclosure.

FIG. 5 is a schematic diagram for explaining an optical cavity structurepertaining to at least one embodiment of the present disclosure.

FIG. 6 is a table illustrating examples of material and film thicknessof layers of the organic EL display panel pertaining to at least oneembodiment of the present disclosure.

FIG. 7A is a graph illustrating variation of a driving voltage with thepassage of a driving time with respect to organic EL elements pertainingto at least one embodiment of the present disclosure, and FIG. 7B is atable illustrating results of experiments on a metal dopant of a secondfunctional layer and a driving voltage stability to verify effects bythe organic EL elements pertaining to at least one embodiment of thepresent disclosure.

FIG. 8 is a flowchart illustrating a manufacturing process of theorganic EL display panel pertaining to at least one embodiment of thepresent disclosure.

FIG. 9A to FIG. 9D are partial cross-section diagrams schematicallyillustrating the manufacturing process of the organic EL display panelpertaining to at least one embodiment of the present disclosure.

FIG. 10A to FIG. 10D are partial cross-section diagrams, continuing fromFIG. 9D, schematically illustrating the manufacturing process of theorganic EL display panel pertaining to at least one embodiment of thepresent disclosure.

FIG. 11A and FIG. 11B are partial cross-section diagrams, continuingfrom FIG. 10D, schematically illustrating the manufacturing process ofthe organic EL display panel pertaining to at least one embodiment ofthe present disclosure.

FIG. 12A to FIG. 12D are partial cross-section diagrams, continuing fromFIG. 11B, schematically illustrating the manufacturing process of theorganic EL display panel pertaining to at least one embodiment of thepresent disclosure.

FIG. 13A to FIG. 13G are cross-section diagrams schematicallyillustrating a process of manufacturing a color filter substrateseparately pertaining to at least one embodiment of the presentdisclosure in organic EL display panel manufacturing.

FIG. 14A and FIG. 14B are cross-section diagrams, continuing from FIG.13G, schematically illustrating the manufacturing process of the organicEL display panel pertaining to at least one embodiment of the presentdisclosure.

FIG. 15 is a diagram schematically illustrating a layered structure oforganic EL elements pertaining to at least one embodiment of the presentdisclosure.

FIG. 16 is a diagram schematically illustrating a layered structure oforganic EL elements pertaining to at least one embodiment of the presentdisclosure.

FIG. 17 is a diagram schematically illustrating a layered structure oforganic EL elements pertaining to at least one embodiment of the presentdisclosure.

FIG. 18 is a diagram schematically illustrating a layered structure oforganic EL elements pertaining to at least one embodiment of the presentdisclosure.

FIG. 19 is a diagram schematically illustrating a layered structure oforganic EL elements pertaining to at least one embodiment of the presentdisclosure.

FIG. 20 is a schematic cross-section diagram illustrating an organic ELdisplay panel pertaining to at least one embodiment of the presentdisclosure.

FIG. 21 is a schematic cross-section diagram for describing a problem ina conventional organic EL display panel.

DETAILED DESCRIPTION

<<Process by which One Aspect of the Present Disclosure was Achieved>>

In the case where an optical cavity structure is adopted as in the aboveInternational Publication No. WO2015/194189 (hereinafter, referred to asPatent Literature 1), film thicknesses of organic light-emitting layers,hole injection transport layers, and so on differ between light emissioncolors, and accordingly amounts of moisture and so on remaining in thelayers differ between the light emission colors. Due to this, adeterioration degree of Ba in electron injection transport layers at theinitial stage, during storage, and during electric current applicationdiffers between the light emission colors.

As a result, a luminance varies between the light emission colors, andthus a color tone of color images to be displayed varies. This mightmake a viewer to feel that image quality has deteriorated in earlierthan expected.

FIG. 21 is a schematic cross-section diagram illustrating a layeredstructure of an organic EL display panel pertaining to Patent Literature1 described above. In the figure, reference numerals 500R, 500G, and500B indicate subpixels emitting light of red (R), green (G), and blue(B) colors, respectively.

The subpixels 500R, 500G, and 500B are partitioned by banks 514 formedabove a substrate 511, and each include an organic EL element. Eachorganic EL element includes an anode 513, a hole injection transportlayer 516, an organic light-emitting layer 517, an NaF layer 518, anelectron injection transport layer 519, and a cathode 520 which aredisposed in this order from the substrate 511.

Further, a sealing layer and so on are layered above the cathodes 520,though not illustrated here.

As illustrated in FIG. 21, the hole injection transport layers 516 andthe organic light-emitting layers 517 have respective film thicknesseswhich increase in the order of the B, G, and R light emission colors aswavelengths increase in this order, and these layers have structuressuch that luminous efficiency is improved by the optical cavitystructure.

To form organic layers having film thicknesses differing between thelight emission colors, a wet process by a printing method is oftenadopted. According to the wet process, it is easy to perform separateapplication for each light emission color, thereby significantlysimplifying a working process and also exhibiting a high use efficiencyof materials compared with a dry process. This helps to reduceproduction costs.

The electron injection transport layers 519 are formed by doping anorganic material having electron transport properties with Ba having alow work function. In many cases, there is a large difference between anenergy level of the lowest unoccupied molecular orbital (LUMO) of theorganic material included in the organic light-emitting layers 517 and aFermi level of a material of the cathode, and this exhibitsunsatisfactory electron injection properties. In view of this, by dopingan organic material with Ba, which is a metal material having a low workfunction, the electron injection properties are improved, therebyfacilitating transport of electrons from the cathodes 520 to the organiclight-emitting layers 517 and helping to reduce a driving voltage.

By the way, the hole injection transport layers 516 and/or the organiclight-emitting layers 517 formed by the wet process are dried by bakingor the like such that moisture, solvent, and so on (hereinafter,referred to collectively as moisture etc.) inside the layers areremoved. Unfortunately, complete removal of the moisture etc. isdifficult, and a slight amount of the moisture etc. always remainsinside the layers. This moisture etc. diffuses into even the electroninjection transport layers 519, which are upper layers of the holeinjection transport layers 516 and the organic light-emitting layers517, as a driving time of the organic EL elements passes by. Ba, withwhich is doped for forming the electron injection transport layer 519,is chemically active, and accordingly reacts with the moisture etc. tocause the electron injection properties to deteriorate thus to shortenthe operating life.

According to Patent Literature 1 described above, in view of this, theNaF layers 518 are formed, as intermediate layers, between the organiclight-emitting layers 517 and the electron injection transport layers519. A fluoride of an alkali metal such as Na or an alkaline earth metalhas properties of blocking moisture etc., and suppresses penetration ofmoisture etc. from the organic light-emitting layers 517 and so on tothe electron injection transport layers 519, thereby contributing to anincrease of an operating life of organic EL display panels.

Meanwhile, the NaF layers 518 have high insulating properties.Accordingly, parts of the NaF layers 518 which is on the side of thesecond functional layer 19 are reduced by Ba of the electron injectiontransport layer 519 such that the parts dissociate into Na and F. Thisexhibits excellent electron injection properties. In the case where thefilm thickness of the NaF layers 518 is increased in order to improvethe properties of blocking moisture etc., only a small reduction actionof the upper layers exerts on especially lower parts of the intermediatelayers, and thus the driving voltage increases. This insufficientlyachieves the purpose of improving the luminous efficiency.

Thus, the film thickness of the NaF layers 518 has a certain upperlimit, and the properties of blocking moisture etc. of the NaF layers518 also have a limit. In addition, since the banks 514 typicallyinclude a resin material, moisture etc. might pass through the inside ofthe resin material to reach the electron injection transport layer 519.

If an optical cavity structure is not adopted and the film thicknessesof the organic light-emitting layers 517 and the hole injectiontransport layers 516 are set to be uniform among the light emissioncolors, an amount of moisture etc. remaining in these organic layers isalso substantially equal among the light emission colors. When suchmoisture etc. penetrates through the NaF layers 518 and the banks 514 toreact with Ba of the electron injection transport layers 519, a luminousdeterioration amount does not greatly differ between the light emissioncolors. This only makes a viewer to feel a screen has become a littledark. The viewer is unlikely to visually confirm a variation of colortone on a display screen and thus unlikely to feel the image quality hasdeteriorated.

However, in the case where an optical cavity structure is adopted andthe hole injection transport layer 516 and the organic light-emittinglayers 517 are formed so as to have film thicknesses differing betweenthe R, G, and B colors, as the film thickness increases, a larger amountof moisture etc. remains inside the layers and thus reaches the electroninjection transport layers 519 via the NaF layers 518 and the banks 514.Thus, the deterioration degree of the electron injection properties ofBa increases in the order of the B, G, and R colors, and this causes adifference in deterioration amount of luminance. Thus, reproduced colorimages have variation in color tone, and this makes a user to easilyfeel deterioration in image quality early and thus might shorten theproduct operating life.

Such a problem might occur not only in organic EL display panels usingorganic EL elements as light-emitting elements but also in displaypanels typically including self-luminous elements and including organicfunctional layers formed by a wet process to construct an optical cavitystructure such as quantum dot display panels including light-emittinglayers formed from quantum dot light-emitting diodes (QLEDs).

In order to solve the above problem, the present inventors earnestlyconducted researches for seeking a display panel with a prolongedproduct operating life while adopting a wet process to reduce costs,adopting an optical cavity structure to improve a luminous efficiency,and suppressing early variation in color tone. As a result, the presentinventors achieved at least one aspect of the present disclosure.

<<Outline of at Least One Aspect of the Present Disclosure>>

A display panel pertaining to at least one aspect of the presentdisclosure is a display panel in which pixels each includinglight-emitting parts are two-dimensionally arranged across a mainsurface of a substrate. The light-emitting parts each include: a firstelectrode that is light-reflective; a first functional layer that isdisposed above the first electrode; a light-emitting layer that isdisposed above the first functional layer; a second functional layerthat is disposed above the light-emitting layer and includes ytterbium;and a second electrode that is disposed above the second functionallayer and is light-transmissive. At least one of the light-emittinglayer and the first functional layer is an applied film. With respect toeach of the pixels, at least one of the light-emitting parts differsfrom any other of the light-emitting parts in terms of light emissioncolor, and the at least one light-emitting part differs from the anyother of the light-emitting parts in terms of film thickness of at leastone of the light-emitting layer and the first functional layer.

According to this aspect, at least one of the light-emitting layer andthe first functional layer is a layer formed by a wet process toconstruct an optical cavity structure, thereby achieving both a processcost reduction and a luminous efficiency improvement, and obtaining thesecond functional layer doped with ytterbium. Ytterbium is a metalhaving a low work function but is chemically stable. Compared with Baand so on, ytterbium has a low reactivity with moisture etc., andaccordingly electron injection properties are unlikely to deteriorate.For this reason, the above aspect helps to provide a display panel thatachieves both a process cost reduction and a luminous efficiencyimprovement by constructing an optical cavity structure using the wetprocess and also has a less luminance variation between the lightemission colors thus to have a long product operating life.

According to the display panel pertaining to at least one aspect of thepresent disclosure, the light-emitting parts each further include anintermediate layer that is disposed between the light-emitting layer andthe second functional layer, and includes a fluoride of a metal selectedfrom alkali metals or alkaline earth metals.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the light-emitting parts each further includean intermediate layer that is disposed between the light-emitting layerand the second functional layer, and is a single ytterbium layer.

Deposition of the intermediate layer between the light-emitting layerand the second functional layer helps to suppress diffusion of moistureetc. remaining in the first functional layer including the applied filmto the second functional layer, and suppress deterioration of ytterbiumwhich is a metal dopant, thereby resulting in a less luminance variationbetween the light emission colors.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the second functional layer includes anorganic material doped with ytterbium.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, a doping concentration of the ytterbiumranges from 3 wt % to 60 wt %.

Setting the doping concentration of the ytterbium to range from 3 wt %to 60 wt % achieves necessary electron injection properties, and alsoavoids a decrease in light-transmissivity of the second functional layerand thus avoids a luminous efficiency deterioration. Also, since thesecond functional layer is formed by doping an organic material with anecessary amount of ytterbium, the film thickness of the secondfunctional layer is increased, thereby increasing a degree of freedom indesigning optical cavity structure.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the second functional layer is a singleytterbium layer.

According to this aspect, since the second functional layer is formedfrom only ytterbium, a manufacturing process is easy and stable electroninjection properties are achieved.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the second functional layer includesytterbium and a fluoride of a metal selected from alkali metals oralkaline earth metals.

According to this aspect, since the second functional layer, which hasboth properties of blocking moisture etc. which are exhibited by afluoride of a metal selected from alkali metals or alkaline earth metalsand electron injection properties exhibited by ytterbium, is obtained,no intermediate layer needs to be provided separately.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the light-emitting parts each further includea light-transmissive and electrically-conductive film that is disposedbetween the second functional layer and the second electrode so as to bein contact with the second functional layer, and includes inorganicoxide. Also, according to the display panel pertaining to at least oneaspect of the present disclosure, the light-transmissive andelectrically-conductive film is preferably an indium tin oxide (ITO)film or an indium zinc oxide (IZO) film.

This aspect exhibits an effect of a light transmittance improvementowing to oxidization of part of Yb included in the second functionallayer in manufacturing a display panel. Also, adjustment of the filmthickness of the light-transmissive and electrically-conductive filmfacilitates construction of an optical cavity structure. Especially anITO film and an IZO film have an excellent electrical conductivity, andaccordingly do not hinder electron injection properties.

Also, according to the display panel pertaining to at least one aspectof the present disclosure, the first electrode is a light-reflectiveanode, and the second electrode is a light-semitransmissive cathode.

This aspect helps to provide a display panel of a top-emission typeincluding an optical cavity structure having a further excellentluminous efficiency. In the display panel of the top-emission type,drive circuits including TFTs and so on are not disposed in a lightemission direction such that an aperture ratio in each light-emittingpart increases and thus an excellent luminous efficiency is exhibited.

Also, a display panel manufacturing method pertaining to at least oneaspect of the present disclosure is a method of manufacturing a displaypanel in which pixels each including light-emitting parts aretwo-dimensionally arranged across a main surface of a substrate. Themethod includes, for each of the light-emitting parts: forming a firstelectrode above the substrate; forming a first functional layer abovethe first electrode; forming a light-emitting layer above the firstfunctional layer; forming a second functional layer above thelight-emitting layer; and forming a second electrode above the secondfunctional layer. One of the first electrode and the second electrode isa light-reflective electrode, and the other is a light-transmissiveelectrode. Out of the first functional layer and the second functionallayer, one functional layer that is disposed between thelight-reflective electrode and the light-emitting layer includesytterbium. At least one of the light-emitting layer and the otherfunctional layer out of the first functional layer and the secondfunctional layer is formed by an application method. With respect toeach of the pixels, at least one of the light-emitting parts differsfrom any other of the light-emitting parts in terms of light emissioncolor, and the at least one light-emitting part differs from the anyother of the light-emitting parts in terms of film thickness of at leastone of the light-emitting layer and the other functional layer out ofthe first functional layer and the second functional layer.

This aspect helps to manufacture a display panel exhibiting an excellentluminous efficiency, displaying high-quality images, and having a longoperating life.

Note that in at least one embodiment of the present disclosure above,the term “above” does not indicate an upper direction (upward in thevertical direction) in an absolute spatial awareness, but is defined bya relative relationship in a layered structure of the light-emittingpart. Specifically, a direction that is perpendicular to the mainsurface of the substrate of the light-emitting part and is toward thesecond electrode from the first electrode is defined as an upperdirection. In addition, for example an expression “above a firstelectrode” indicates not only a region in direct contact with the firstelectrode but also an upper region over the first electrode via alaminate.

Embodiments

The following describes a display panel pertaining to at least oneaspect of the present disclosure by using an example of an organic ELdisplay panel, with reference to the drawings. Note that the drawingsmay be schematic, and are not necessarily to scale.

1. Overall Structure of Organic EL Display Device 1

FIG. 1 a block diagram illustrating the overall structure of an organicEL display device 1. The organic EL display device 1 is a display devicewhich is used for example for a television, a personal computer, amobile terminal, or a display for business purposes such as anelectronic signboard and a large screen for a commercial facility.

The organic EL display device 1 includes an organic EL display panel 10(hereinafter, referred to simply as display panel 10) and a drivecontroller 200 which is electrically connected to the display panel 10.

According to the present embodiment, the display panel 10 is a topemission type display panel, a top surface of which is a rectangularimage display surface. In the display panel 10, a plurality of organicEL elements (not illustrated) are arranged across the image displaysurface, and an image is displayed by combining light emission of theorganic EL elements. As an example, the display panel 10 employs anactive matrix system.

The drive controller 200 includes drive circuits 210 connected to thedisplay panel 10 and a control circuit 220 connected to an externaldevice such as a computer or a receiving device such as an antenna. Thedrive circuits 210 include power supply circuits for supplying electricpower to the organic EL elements, signal circuits for applying a voltagesignal for controlling the electric power supplied to the organic ELelements, a scanning circuit for switching a position to which thevoltage signal is applied at regular intervals, and the like.

The control circuit 220 controls operations of the drive circuits 210 inaccordance with data including image information input from the externaldevice or the receiving device.

In FIG. 1, as an example, four of the drive circuits 210 are disposedaround the display panel 10, but the structure of the drive controller200 is not limited to this example, and the number and position of thedrive circuits 210 may be modified as appropriate. For the sake ofexplanation, as illustrated in FIG. 1, a direction along a long side ofa top surface of the display panel 10 is referred to as X direction anda direction along a short side of the top surface of the display panel10 is referred to as Y direction.

2. Structure of Display Panel 10

(A) Plan View Structure

FIG. 2 is a schematic enlarged plan view illustrating part of the imagedisplay surface of the display panel 10. According to the display panel10, as an example, subpixels 100R, 100G, and 100B are arranged in amatrix. In the subpixels 100R, 100G, and 100B, organic EL elements(light-emitting parts) which respectively emit light of red (R), green(G), and blue (B) colors (hereinafter, also referred to simply as R, G,and B) are arranged. The subpixels 100R, 100G, and 100B are lined upalternating in the X direction (row direction), and a set of thesubpixels 100R, 100G, and 100B in the X direction constitute one pixelP. Through combining gradation control of luminance of the subpixels100R, 100G, and 100B, full color is possible.

In addition, in the Y direction (column direction), the subpixels 100R,100G, and 100B are arranged to form subpixel columns CR, CG, and CB,respectively, in which only the corresponding color of subpixels arepresent. As a result, across the display panel 10, the pixels P arearranged in a matrix along the X direction and the Y direction, and animage is displayed on the image display surface through a combination ofcolors of light emitted by the pixels P.

In the subpixels 100R, 100G, and 100B, the organic EL elements 2(R),2(G), and 2(B), which respectively emit light of the R, G, and B colors,are respectively arranged (see FIG. 4).

Respective ranges of the subpixels 100R, 100G, and 100B are defined bybanks (column banks) 14 and pixel partition layers (row banks) 141.

The display panel 10 pertaining to the present embodiment employs aso-called line bank structure.

FIG. 3 is a partial perspective diagram of the display panel 10pertaining to at least one embodiment for explaining how the banks 14and the pixel partition layers 141 are formed. As illustrated in thefigure, the pixel partition layers 141 have a height sufficiently lowerthan the banks 14. As described later, when organic light-emittinglayers 17 and so on are formed by a printing method, liquid surfaces ofink have a height higher than the pixel partition layers 141. Thisallows the ink to flow in the column direction (Y direction) in orderfor the liquid surfaces of the ink to be levelled, thereby makingvariation of film thicknesses in the column direction smaller.

The subpixel columns CR, CG, and CB are partitioned by the banks 14 atintervals in the X direction, and in each of the subpixel columns CR,CG, and CB, the subpixels 100R, 100G, or 100B therein share a continuousorganic light-emitting layer.

However, in each of the subpixel columns CR, CG, and CB, the pixelpartition layers 141 are disposed at intervals in the Y direction toinsulate the subpixels 100R, 100G, and 100B from each other, such thateach of the subpixels 100R, 100G, and 100B can emit light independently.

The banks 14 and the pixel partition layers 141 are indicated by dottedlines in FIG. 2. This is because the banks 14 and the pixel partitionlayers 141 are not exposed on the surface of the image display surfaceand are disposed inside the image display surface.

(B) Cross-Section Structure

FIG. 4 is a schematic cross-section diagram taken along a line A-A inFIG. 2.

The display panel 10 includes pixels which are each composed of threesubpixels each emitting light of a different one of the R, G, and Bcolors. The three subpixels, namely the subpixels 100R, 100G, and 100Bare respectively composed of organic EL elements 2(R), 2(G), and 2(B)emitting light of a corresponding color.

The organic EL elements 2(R), 2(G), and 2(B), which respectively emitlight of the R, G, and B colors, basically have the same structure, andthus are referred collectively to as organic EL elements 2 when they arenot distinguished from one another.

As illustrated in FIG. 4, the display panel 10 includes a substrate 11,an interlayer insulating layer 12, pixel electrodes (anodes) 13, banks14, first functional layers 22 (hole injection layers 15 and holetransport layers 16), organic light-emitting layers 17, an intermediatelayer 18, a second functional layer 19, a counter electrode (cathode)20, a sealing layer 21, and a color filter (CF) substrate 30.

(1) Substrate

The substrate 11 includes a base material 111 which is an insulatingmaterial and a thin film transistor (TFT) layer 112. The TFT layer 112has a driving circuit formed therein for each subpixel. The basematerial 111 is for example a glass substrate, a quartz substrate, asilicon substrate, or a metal substrate including molybdenum sulfide,copper, zinc, aluminum, stainless, magnesium, iron, nickel, gold, andsilver, a semiconductor substrate including gallium arsenide, or aplastic substrate.

A plastic substrate is usable to form a flexible display panel. Eitherthermoplastic resin or thermosetting resin is usable as material of theplastic substrate. The plastic material may be for example a laminate ofany one type or any two or more types of the following materials,including polyethylene, polypropylene, polyamide, polyimide (PI),polycarbonate, acrylic resin, polyethylene terephthalate (PET),polybutylene terephthalate, polyacetal, other fluororesin, thermoplasticelastomer such as styrene elastomer, polyolefin elastomer, polyvinylchloride elastomer, polyurethane elastomer, fluorine rubber elastomer,and chlorinated polyethylene elastomer, epoxy resin, unsaturatedpolyester, silicone resin, polyurethane, or copolymer, blend, polymeralloy or the like mainly including such a material described above.

(2) Interlayer Insulating Layer

The interlayer insulating layer 12 is formed on the substrate 11. Theinterlayer insulating layer 12 includes a resin material and is forflattening irregularities in a top surface of the TFT layer 112. Theresin material is for example a positive photosensitive material.Examples of the photosensitive material include acrylic resin, polyimideresin, siloxane resin, and phenolic resin. Also, although notillustrated in the cross-section in FIG. 4, the interlayer insulatinglayer 12 has a contact hole provided therein for each subpixel.

(3) Pixel Electrodes (First Electrodes)

The pixel electrodes 13 include metal layers including alight-reflective metal material, and are formed on the interlayerinsulating layer 12. The pixel electrode 13 is formed for each subpixel,and is electrically connected with the TFT layer 112 via a contact hole(not illustrated).

In the present embodiment, the pixel electrode 13 functions as an anode.

Specific examples of the light-reflective metal material include silver(Ag), aluminum (Al), alloy of aluminum, molybdenum (Mo), alloy ofsilver, palladium, and copper (APC), alloy of silver, rubidium, and gold(ARA), alloy of molybdenum and chromium (MoCr), alloy of molybdenum andtungsten (MoW), and alloy of nickel and chromium (NiCr).

In at least one embodiment, the pixel electrodes 13 are single metallayers. In at least one embodiment, the pixel electrodes 13 have alayered structure including a metal oxide layer such as an indium tinoxide (ITO) layer and an indium zinc oxide (IZO) layer layered on ametal layer.

(4) Banks and Pixel Partition Layers

The banks 14 partition the pixel electrodes 13 corresponding to thesubpixels on the substrate 11 into columns in the X direction (see FIG.2), and each have a line bank shape extending in the Y direction betweenthe subpixel columns CR, CG, and CB in the X direction.

An electrically-insulating material is used for the banks 14. Specificexamples of the electrically-insulating material include an insulatingorganic material such as acrylic resin, polyimide resin, novolac resin,and phenolic resin.

In the case where the organic light-emitting layers 17 are formed by anapplication method, the banks 14 function as a structure for preventingan ink mixture between subpixels in each pixel.

From the viewpoint of workability, in at least one embodiment, when aresin material is used for the banks 14, a photosensitive resin materialis used. Photosensitivity of the resin material may be either positiveor negative.

In at least one embodiment, the banks 14 are resistant to organicsolvents and heat. Also, in at least one embodiment, the banks 14 haveliquid-repellent surfaces in order to suppress an ink overflow.

Where the pixel electrodes 13 are not formed, bottom surfaces of thebanks 14 are in contact with a top surface of the interlayer insulatinglayer 12.

The pixel partition layers 141 include an electrically-insulatingmaterial, and cover end parts in the Y direction (FIG. 2) of the pixelelectrodes 13 in each sub pixel column, partitioning the pixelelectrodes 13 in the Y direction.

Film thickness of the pixel partition layers 141 is set to be slightlylarger than film thickness of the pixel electrodes 13 but to be smallerthan film thickness of the organic light-emitting layers 17 includingtheir top surfaces. Thus, the organic light-emitting layers 17 in thesubpixel columns CR, CG, and CB are not partitioned by the pixelpartition layers 141, and accordingly flow of ink is not disturbed whenforming the organic light-emitting layers 17. This facilitates the filmthickness of each of the organic light-emitting layers 17 to be uniformwithin the corresponding subpixel column.

With the structure described above, the pixel partition layers 141improve electrical insulation between the pixel electrodes 13 in the Ydirection and also have functions of suppressing discontinuity of theorganic light-emitting layers 17 within any given one of the subpixelcolumns CR, CG, and CB, improving electrical insulation between thepixel electrodes 13 and the counter electrode 20, and so on.

Specific examples of the electrically-insulating material used for thepixel partition layers 141 include a resin material exemplified as thematerial of the banks 14 and an inorganic material.

(5) First Functional Layers

In the present embodiment, the first functional layers 22 each includetwo layers, namely, the hole injection layer 15 and the hole transportlayer 16.

(5-1) The hole injection layers 15 are provided on the pixel electrodes13 in order to promote injection of holes from the pixel electrodes 13to the organic light-emitting layers 17. In the present embodiment, toform the hole injection layers 15 by a wet process, the hole injectionlayers 15 mainly include an electrically-conductive polymer materialsuch as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT/PSS), an oligomer material, or a low-molecular material.

(5-2) Hole Transport Layers

The hole transport layers 16 have a function of transporting holesinjected from the hole injection layers 15 to the organic light-emittinglayers 17. The hole transport layers 16 are formed by a wet processusing for example a high-molecular compound having no hydrophilic groupsuch as polyfluorene, polyfluorene derivative, polyallylamine, andpolyallylamine derivative, or a low-molecular compound having nohydrophilic group and including a similar material.

(6) Organic Light-Emitting Layers

The organic light-emitting layers 17 are formed inside the openings 14 a(FIG. 3), and each have a function of emitting light of R, G, or B colorowing to recombination of holes and electrons. In particular, when it isnecessary to specify the light emission color for explanation, theorganic light-emitting layers 17 are referred to as the organiclight-emitting layers 17(R), 17(G), and 17(B) separately.

Publicly-known materials are usable for a material of the light-emittinglayers 17.

Specific examples of the material of the organic light-emitting layers17 include phosphor such as oxinoid compound, perylene compound,coumarin compound, azacoumarin compound, oxazole compound, oxadiazolecompound, perinone compound, pyrrolopyrrole compound, naphthalenecompound, anthracene compound, fluorene compound, fluoranthene compound,tetracene compound, pyrene compound, coronene compound, quinolonecompound and azaquinolone compound, pyrazoline derivative and pyrazolonederivative, rhodamine compound, chrysene compound, phenanthrenecompound, cyclopentadiene compound, stilbene compound, diphenylquinonecompound, styryl compound, butadiene compound, dicyanomethylenepyrancompound, dicyanomethylenethiopyran compound, fluorescein compound,pyrylium compound, thiapyrylium compound, selenapyrylium compound,telluropyrylium compound, aromatic aldadiene compound, oligophenylenecompound, thioxanthene compound, cyanine compound, acridine compound,and metal complex of 8-hydroxyquinoline compound, metal complex of2-bipyridine compound, complex of a Schiff base and group III metal,oxine metal complex, and rare earth complex.

(7) Intermediate Layer

The intermediate layer 18 has a function of suppressing movement ofmoisture etc. from the organic layers provided thereunder to the secondfunctional layer 19, and a function of transporting electrons from thecounter electrode 20 to the organic light-emitting layers 17.

In the present embodiment, the intermediate layer 18 includes sodiumfluoride (NaF). NaF has a low moisture permeability and haswaterproofing properties. Contact of NaF with a reducing material (Yb inthe present embodiment) causes contact parts of NaF to dissociate intoNa and F, thereby obtaining excellent electron injection properties. Inat least one embodiment, the intermediate layer 18 includes a fluorideof a metal selected from other alkali metals or alkaline earth metals(for example, Li).

(8) Second Functional Layer

The second functional layer 19 has a function of injecting andtransporting electrons supplied from the counter electrode 20 toward theorganic light-emitting layers 17. In the present embodiment, the secondfunctional layer 19 includes an organic material, in particular, anorganic material having electron transport properties, doped withytterbium (Yb).

This structure helps to stabilize electron injection properties of thesecond functional layer 19. Accordingly, when the hole injection layers15, the hole transport layers 16, and/or the organic light-emittinglayers 17 are formed by a wet process so as to have different filmthicknesses between the light emission colors in order to construct anoptical cavity structure, the electron injection properties are notinfluenced greatly. This avoids a color tone variation caused by adifference in degree of deterioration between the light emission colors,and thus makes a viewer not to feel the operating life is short. Thedetails will be described later.

The organic material (host material) having electron transportproperties is for example a π-electron low molecular organic materialsuch as oxadiazole derivative (OXD), triazole derivative (TAZ), andphenanthroline derivative (BCP, Bphen), but is not limited to these.

(9) Counter Electrode (Second Electrode)

The counter electrode 20 includes a light-transmissive andelectrically-conductive material, and is formed on the second functionallayer 19. The counter electrode 20 functions as a cathode.

In the present embodiment, the counter electrode 20 has a two-layerstructure and is formed by layering a metal thin film 20B on alight-transmissive and electrically-conductive film 20A including metaloxide such as ITO or IZO.

In at least one embodiment, to obtain an optical cavity structurefurther effectively, the metal thin film 20B of the counter electrode 20includes at least one material selected from the group consisting ofaluminum, magnesium, silver, aluminum-lithium alloy, magnesium-silveralloy, and the like, and has a half mirror structure(light-semitransmissivity). In at least one embodiment, the metal thinfilm 20B in this case has a film thickness from 5 nm to 30 nm.

Also, adjustment of a film thickness of the light-transmissive andelectrically-conductive film 20A helps to set an optical distancebetween the organic light-emitting layers 17 and a reflective surface ofthe metal thin film 20B to an appropriate length, thereby obtaining aneffective optical cavity structure. In at least one embodiment, alight-transmissive and electrically-conductive film including forexample ITO or IZO is formed on the counter electrode 20, therebyadjusting chromaticity and viewing angle.

(10) Sealing Layer

The sealing layer 21 is provided for preventing the metal thin film 20Bof the counter electrode 20 and organic layers including the IZO film20A, the hole transport layers 16, the organic light-emitting layers 17,and the second functional layer 19 from being exposed to moisture, air,and so on and thus from being deteriorated.

The sealing layer 21 for example includes a light-transmissive materialsuch as silicon nitride (SiN) and silicon oxynitride (SiON).

(11) CF Substrate

The CF substrate 30 is attached onto the sealing layer 21 via a joininglayer 34. The CF substrate 30 includes color filter layers 32 forcorrecting chromaticity of light emitted from the organic EL elements 2.The CF substrate 30 helps to further protect the hole transport layers16, the organic light-emitting layers 17, the second functional layer19, and so on against external moisture, air, and so on.

3. Principle of Optical Cavity Structure and Examples of Film Thicknessin Organic EL Elements

As described above, in at least one embodiment, an optical cavitystructure is constructed in order to improve the luminous efficiency ofthe organic EL elements 2.

FIG. 5 is a schematic diagram for explaining optical interference in anoptical cavity structure of the organic EL elements 2. An optical cavitystructure is formed between an interface of the pixel electrodes 13 withthe hole injection layers 15 and an interface between the metal thinfilm 20B and the light-transmissive and electrically-conductive film 20Awhich are included in the counter electrode 20.

Note that the explanation is provided on the figure based on theassumption that a point of light emission owing to recombination ofholes and electrons is near an interface between the organiclight-emitting layers 17 and the hole transport layers 16.

In FIG. 5, an optical path C₁ is an optical path along which lightemitted from the organic light-emitting layers 17 toward the counterelectrode 20 directly transmits through the counter electrode 20 withoutbeing reflected.

An optical path C₂ is an optical path along which light emitted from theorganic light-emitting layers 17 toward the pixel electrodes 13 isreflected by the pixel electrodes 13, and transmits through the counterelectrode 20 via the organic light-emitting layers 17.

An optical path C₃ is an optical path along which light emitted from theorganic light-emitting layers 17 toward the counter electrode 20 isreflected by the metal thin film 20B (which is light-semitransmissive)of the counter electrode 20, is further reflected by the pixelelectrodes 13, and then transmits through the counter electrode 20 viathe organic light-emitting layers 17.

In the optical cavity structure, respective optical distances of theoptical paths C₁, C₂, and C₃ are set such that resonance occurs amonglight emitted along these optical paths. Here, the optical distance ofthe optical path is the sum of products of film thickness and refractiveindex in each of the layers through which light transmits. Since thewavelength differs between the light emission colors, the respectivefilm thicknesses of the hole injection layers 15, the hole transportlayers 16, the organic light-emitting layers 17, the second functionallayer 19, the light-transmissive and electrically-conductive film 20Aand so on are determined according to the wavelength.

FIG. 6 is a table illustrating a layered structure including every layerfrom the pixel electrodes 13 to the counter electrode 20 in the organicEL elements 2 pertaining to the present embodiment and specific examplesof film thickness of each layer expressed in nm. Numerical values on theright outside the table indicate that a settable range of the total filmthickness. For example, the total film thickness of the hole injectionlayers 15, the hole transport layers 16, and the organic light-emittinglayers 17 is indicated to be settable within a range of 50 nm to 300 nm.

Note that the film thicknesses illustrated in the table in FIG. 6 arejust examples, and are not limited to these values. A person skilled inthe art would appropriately design the film thicknesses according to thespecifications of organic EL elements, refractive indexes of materialsto be used, and so on.

4. Assessment Test

FIG. 7A is a graph illustrating a typical relationship between a drivingtime (h) of the organic EL elements and a voltage to be applied(hereinafter, referred to as driving voltage) (V) which is necessary toperform control (constant current control) to supply the organic ELelements with a constant electric current.

In the graph of FIG. 7A, a horizontal axis indicates the driving time, avertical axis indicates the driving voltage, and a curve L indicatesvariation of the driving voltage with the passage of the driving time.As illustrated in the figure, the driving voltage V gradually varied atlow values at the driving beginning (part R), but rapidly rose after acertain time has passed by (part Q).

Here, regarding an approximate straight-line Lr in the part R at thebeginning of driving (beginning of life) in the curve L and anapproximate straight-line Lq in the part Q at the end of driving (end oflife) in the curve L, an intersection point of these approximatestraight-lines is defined as an inflection point P.

Then, an experiment of measuring a time necessary to reach theinflection point P was performed at an environmental temperature of 90°C. at different doping concentrations of Ba and Yb as a metal dopant ofthe second functional layer 19 (acceleration test). In this experiment,samples of organic EL elements having the same structure as the layeredstructure of the subpixels R in FIG. 6 were used.

FIG. 7B is a table illustrating results of the experiment. In the table,column “inflection point (h)” indicates a time necessary to reach theinflection point P since start of driving the organic EL elements(inflection point arrival time). Also, column “inflection point(relative value)” indicates a relative value in % of the inflectionpoint arrival time under various conditions in the case where aninflection point arrival time of Ba as the metal dopant at the dopingconcentration of 40 wt % was set to “1”.

As illustrated in the table of FIG. 7B, in the case where Ba was used asthe metal dopant of the second functional layer 19, the inflection pointarrival time reached only 220 hours even at its maximum dopingconcentration of 40 wt %. Meanwhile, in the case where Yb was used asthe metal dopant, the inflection point arrival time already reached 210hours at its doping concentration of 20 wt %, and reached 400 hours atits doping concentration of 40 wt %, which is larger by 182% than thecase where the metal dopant was Ba.

As illustrated in FIG. 7A, until the inflection point arrival time haspassed by, variation of the driving voltage was relatively gradual.Accordingly, the results of the experiment indicate that as theinflection point arrival time increases, a degree of deterioration ofelectron injection properties of the metal dopant decreases. It isassessed that the larger the inflection point arrival time is, the morestable the electron injection properties are.

Thus, by adopting Yb as the metal dopant of the second functional layer19, the electron injection properties are much more stabilized thanconventional cases where Ba is used as the metal dopant. This suppressesvariation in driving voltage between the light emission colors due tothe difference in film thickness of the first functional layers 22 andthe organic light-emitting layers 17 in the optical cavity structurebetween the light emission colors, thereby suppressing deterioration inimage quality to prolong the product operating life.

5. Method of Manufacturing Display Panel

The following describes a method of manufacturing the display panel 10pertaining to at least one aspect of the present disclosure, withreference to the drawings.

FIG. 8 is a flowchart illustrating a manufacturing process of thedisplay panel 10. FIG. 9A to FIG. 9D, FIG. 10A to FIG. 10D, FIG. 11A,FIG. 11B, FIG. 12A to FIG. 12D, FIG. 13A to FIG. 13G, FIG. 14A, and FIG.14B are schematic cross-section diagrams illustrating processes inmanufacturing the display panel 10.

(1) Substrate Preparing Process

First, as illustrated in FIG. 9A, a substrate 11 is prepared by forminga TFT layer 112 on a base material 111 (FIG. 8: Step S1). The TFT layer112 can be formed by a known TFT manufacturing method.

(2) Interlayer Insulating Layer Forming Process

Next, as illustrated in FIG. 9B, an interlayer insulating layer 12 isformed on the substrate 11 (FIG. 8: Step S2).

Specifically, a resin material having a constant fluidity is appliedacross a top surface of the substrate 11 by for example die coating soas to fill irregularities in the substrate 11 caused by the TFT layer112. Thus, a top surface of the interlayer insulating layer 12 has aflattened shape conforming to a top surface of the base material 111.

Also, dry-etching is performed on parts of the interlayer insulatinglayer 12 above TFT elements, for example source electrodes, to providecontact holes (not illustrated). The contact holes are provided bypatterning or the like such that surfaces of the source electrodes areexposed at bottoms of the contact holes.

Next, connection electrode layers are formed along inner walls of thecontact holes. Upper parts of the connection electrode layers arepartially disposed on the interlayer insulating layer 12. The connectionelectrode layers can be formed by forming a metal film by for examplesputtering, and then patterning the metal film by photolithography andwet etching.

(3) Pixel Electrode Forming Process

Next, as illustrated in FIG. 9C, a pixel electrode material layer 130 isformed on the interlayer insulating layer 12. The pixel electrodematerial layer 130 can be formed by vacuum deposition, sputtering, orthe like.

Then, as illustrated in FIG. 9D, the pixel electrode material layer 130is patterned by etching to form a plurality of pixel electrodes 13partitioned for each subpixel (FIG. 8: Step S3).

(4) Bank and Pixel Partition Layer Forming Process

Next, banks 14 and pixel partition layers 141 are formed (FIG. 8: StepS4).

In the present embodiment, the pixel partition layers 141 and the banks14 are formed through separate processes.

(4-1) Pixel Partition Layer Formation

First, the pixel partition layers 141 extending in the X direction areformed so as to partition pixel electrode columns extending in the Ydirection (FIG. 2) for each subpixel.

As illustrated in FIG. 10A, a pixel partition layer material layer 1410is formed by uniformly applying a photosensitive resin material which isa material of the pixel partition layers 141 onto the interlayerinsulating layer 12 on which the pixel electrodes 13 are formed. Here,an application amount of the resin material has been determined inadvance such that the pixel partition layer material layer 1410 afterdrying has a desired film thickness of the pixel partition layers 141.

A method of applying the resin material is specifically for example awet process such as die coating, slit coating, and spin coating. In atleast one embodiment, by for example vacuum drying and low-temperatureheating at an approximate temperature of 60° C. to 120° C. (pre-baking)after application, an unnecessary solvent is removed, and also the pixelpartition layer material layer 1410 is fixed onto the interlayerinsulating layer 12.

Then, the pixel partition layer material layer 1410 is patterned byphotolithography.

For example, in the case where the pixel partition layer material layer1410 has positive photosensitivity, exposure is performed on the pixelpartition layer material layer 1410 via a photomask (not illustrated).The photomask shields parts of the pixel partition layer material layer1410 to remain as the pixel partition layers 141 against light and haslight-transmissive parts corresponding to parts of the pixel partitionlayer material layer 1410 to be removed.

Next, developing is performed, and the exposed parts of the pixelpartition layer material layer 1410 are removed. Thus, the pixelpartition layers 141 are formed. Specific examples of developing methodsinclude a method of immersing the entire substrate 11 in a developersuch as an organic solvent and an alkali solution which dissolves partsof the pixel partition layer material layer 1410 which have been exposedto light, and then rinsing the substrate 11 by a rinse solution such aspure water.

Then, the pixel partition layer material layer 1410 is baked(post-baked) at a predefined temperature. As a result, the pixelpartition layers 141 extending in the X direction are formed on theinterlayer insulating layer 12 (FIG. 10B).

(4-2) Bank Formation

Next, the banks 14 extending in the Y direction are formed in the samemanner as the pixel partition layers 141 described above.

Specifically, a bank material layer 140 is formed by applying a resinmaterial for banks by die coating or the like onto the interlayerinsulating layer 12, on which the pixel electrodes 13 and the pixelpartition layers 141 are formed (FIG. 10C). Here, an application amountof the resin material has been determined in advance such that the bankmaterial layer 140 after drying has a desired height of the banks 14.

Then, the bank material layer 140 is patterned to make the banks 14extending in the Y direction by photolithography and is baked at apredefined temperature, completing the banks 14 (FIG. 10D).

In the above process, the respective material layers for the pixelpartition layers 141 and the banks 14 are both formed by a wet processand then are patterned. In at least one embodiment, at least one of therespective material layers for the pixel partition layers 141 and thebanks 14 is formed by a dry process and then is patterned byphotolithography and etching.

(5) First Functional Layer Forming Process

A first functional layer forming process includes formation of holeinjection layers 15 and formation of hole transport layers 16 (FIG. 8:Step S5).

First, the hole injection layers 15 are formed by ejecting inkcontaining an electrically-conductive polymer material such aspoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) fromnozzles 3011 of an application head 301 of a printing device to applythe ink into openings 14 a, volatizing and removing solvent, and/orbaking the solvent.

Then, the hole transport layers 16 are formed by applying ink containingmaterial of the hole transport layers 16 onto the hole injection layers15, volatizing and removing solvent, and/or baking the solvent. Thematerial of the hole transport layers 16 is for example a high-molecularcompound having no hydrophilic group such as polyfluorene, polyfluorenederivative, polyallylamine, and polyallylamine derivative. A method ofapplying the material is the same as in the case of the hole injectionlayers 15.

FIG. 11A is a cross-section diagram illustrating the display panel 10 inthe forming process of the hole transport layers 16 after the formingprocess of the hole injection layers 15. Note that the hole injectionlayers 15 and the hole transport layers 16 have the respective filmthicknesses such as illustrated in the table in FIG. 6 by inkapplication with ink amounts (or both the ink amounts and ink densities)which differ between the light emission colors.

(6) Organic Light-Emitting Layer Forming Process

Next, organic light-emitting layers 17 are formed above the holetransport layers 16 (FIG. 8: Step S6).

Specifically, as illustrated in FIG. 11B, ink containing alight-emitting material of a corresponding light emission color issequentially ejected from the nozzles 3011 of the application head 301of the printing device into the openings 14 a onto the hole transportlayers 16 in the openings 14 a.

Then, the substrate 11 after ink application is carried into a vacuumdry chamber and is heated in a vacuum, thereby evaporating an organicsolvent in the ink. Thus, the organic light-emitting layers 17 areformed.

Note that the organic light-emitting layers 17 have the film thicknessessuch as illustrated in the table in FIG. 6 by ink application with inkamounts (or both the ink amounts and ink densities) which differ betweenthe light emission colors.

(7) Intermediate Layer Forming Process

Next, as illustrated in FIG. 12A, an intermediate layer 18 is formed onthe organic light-emitting layers 17 and the banks 14 (FIG. 8: Step S7).The intermediate layer 18 is formed by forming a film of NaF across allthe subpixels by vapor deposition.

(8) Second Functional Layer Forming Process

Next, as illustrated in FIG. 12B, the second functional layer 19 isformed on the intermediate layer 18 (FIG. 8: Step S8). The secondfunctional layer 19 is formed by for example forming a film byco-deposition using an organic material having electron transportproperties and Yb as a metal dopant across all the subpixels.

In the present embodiment, a doping concentration of Yb is set to 20 wt%.

(9) Counter Electrode Forming Process

Next, a counter electrode 20 is formed on the second functional layer 19(FIG. 8: Step S9).

In a counter electrode forming process, a light-transmissive andelectrically-conductive film (IZO film) 20A is firstly formed on thesecond functional layer 19 by sputtering, and then a metal thin film 20Bis formed on the light-transmissive and electrically-conductive film(IZO film) 20A by forming a film of silver, aluminum, or the like bysputtering, vacuum deposition, or the like (FIG. 12C).

(10) Sealing Layer Forming Process

Next, as illustrated in FIG. 12D, a sealing layer 21 is formed on thecounter electrode 20 (FIG. 8: Step S10). The sealing layer 21 can beformed by forming a film of SiON, SiN, or the like by sputtering, CVD,or the like.

(11) CF Substrate Attaching Process

Next, a CF substrate 30 is formed and is attached onto the sealing layer21 (FIG. 8: Step S11).

FIG. 13A to FIG. 13G are schematic cross-section diagrams illustrating aprocess of manufacturing the CF substrate 30.

First, a light-transmissive upper substrate 31 is prepared, and amaterial of light shielding layers 33 that is primarily an ultravioletcurable resin (for example, ultraviolet curable acrylic resin) materialto which a black pigment is added, is applied on one surface of theupper substrate 31, thereby obtaining a light-shielding layer materiallayer 330 (FIG. 13A).

A pattern mask PM1 having predefined openings is overlaid on a topsurface of the light-shielding layer material layer 330 and isirradiated from above with ultraviolet light (FIG. 13B).

Then, the pattern mask PM1 and uncured parts of the light-shieldinglayer material layer 330 are removed, developing is performed, and thencuring is performed, Thus, the light-shielding layers 33 are completedand each have for example a substantially rectangular shape incross-section (FIG. 13C).

Next, a paste 320G containing material of a color filter, for example agreen (G) color filter, that is primarily an ultraviolet curable resincomponent is applied to a surface of the upper substrate 31 on which thelight-shielding layers 33 are formed (FIG. 13D). Then, a predefinedpattern mask PM2 is placed, and ultraviolet irradiation is performed(FIG. 13E).

Subsequently, curing is performed, the pattern mask PM2 and uncuredparts of the paste 320G are removed, and developing is performed. Thus,a color filter layer 32G is formed (FIG. 13F).

This process illustrated in FIG. 13D to FIG. 13F is repeated similarlyfor each of pastes of red (R) and blue (B) color filters to form colorfilter layers 32(R) and 32(B) (FIG. 13G).

In at least one embodiment, commercially available color filter productsare used, instead of using pastes of the R, G, and B colors. Thus, theCF substrate 30 is formed.

Next, a material of a joining layer 34 that is primarily an ultravioletcurable resin such as acrylic resin, silicone resin, and epoxy resin isapplied to a panel main body which includes every layer from thesubstrate 11 to the sealing layer 21 (FIG. 14A).

Next, the applied material of the joining layer 34 is irradiated withultraviolet light, and the panel main body and the CF substrate 30 arejoined to each other while matching positions relative to each other. Nogas should enter between the panel main body and the CF substrate 30 atthis time. Then, the panel main body and the CF substrate 30 are bakedand thus a sealing process is completed, completing the display panel 10(FIG. 14B).

Note that the above manufacturing method is just an example and can beappropriately modified according to the spirit of the presentdisclosure.

Further, in at least one embodiment, the CF substrate manufacturingprocess has been performed in advance.

<<Modifications>>

Embodiments of an organic EL display panel, an organic EL elementmanufacturing method, and so on have been described as aspects of thepresent disclosure, but the present disclosure is not limited to thedescription above beyond essential characteristic elements thereof. Thefollowing describes other aspects of the present disclosure asmodifications.

(1) Intermediate Layer and Second Functional Layer

(A) In at least one embodiment, the organic EL elements each include amain part (part from the anode to the cathode, hereinafter referred toalso as light-emitting part) which has a layered structure such asillustrated in the schematic diagram in FIG. 15.

The intermediate layer 18 includes NaF, but the present disclosure isnot limited to this. The intermediate layer 18 may include a fluoride ofa metal selected from other alkali metals or alkaline earth metals. Thisis because the fluoride of the selected metal has similar properties ofblocking moisture etc., and the metal belonging to these groups exhibitselectron injection properties when part of the fluoride of metal isreduced by Yb.

In at least one embodiment, the second functional layer 19 includes anorganic material having electron transport properties which is dopedwith Yb at a doping concentration of 20 wt %. However, the presentdisclosure is not limited to this. The doping concentration of Yb mayrange from 3 wt % to 60 wt %.

As described above, since Yb is a substance which is chemically stableand hardly reacts with moisture etc. compared with Ba and the like, Ybdoping even at the doping concentration of 3 wt % can sufficientlyexhibit its electron injection properties.

Also, since Yb has an excellent light-transmissivity compared with Baand the like, Yb doping even at the maximum doping concentration of 60wt % does not have a significant influence on a transmittance of thesecond functional layer 19, and an excellent luminous efficiency can bemaintained.

Yb doping at a high doping concentration can be performed in this way.This helps to maintain the electron injection properties further stablyfor a long period, thereby contributing to a further increase inoperating life. Also, since the range of the Yb doping concentration iswide, it is considered that the organic material as the host material ofthe second functional layer 19 accordingly can be set to have a filmthickness which ranges widely, thereby increasing a degree of freedom indesigning optical cavity structure.

Also, the counter electrode 20 pertaining to at least one embodiment hasa two-layer structure including the light-transmissive andelectrically-conductive film (IZO film) 20A and the metal thin film 20B.However, in the case where an optical path length necessary to constructan optical cavity structure can be provided by varying thickness ofother layer, the light-transmissive and electrically-conductive film(IZO film) 20A is not necessarily essential.

Further, instead of an IZO film, an ITO film which is alight-transmissive and electrically-conductive material including metaloxide likewise, may be used.

(B) Also, in at least one embodiment, the second functional layer 19 isformed by doping an organic material with Yb, but the present disclosureis not limited to this. The second functional layer 19 may be a singleYb layer as illustrated in FIG. 16.

With this structure, the single Yb layer has a further increased liquidresistance and also has an increased Yb effective contact area with NaFof the intermediate layer 18, compared with the layer of the organicmaterial doped with Yb. This promotes a reduction action of NaF by Yb,thereby helping to Na obtained by dissociation to improve the electroninjection properties.

In this case, the second functional layer 19 is formed by forming a Ybfilm on the intermediate layer 18 by vapor deposition or sputtering.

In at least one embodiment, the single Yb layer has a film thicknessfrom 0.1 nm to 10 nm. This is because the single Yb layer having a filmthickness smaller than 0.1 nm might exhibit insufficient electroninjection properties, while the single Yb layer having a film thicknesslarger than 10 nm causes a problem in light-transmissivity and thusmight exhibit a deteriorated luminous efficiency.

(C) Also, the intermediate layer 18 may be a single Yb layer asillustrated in FIG. 17 instead of an NaF single layer. As describedabove, since Yb hardly reacts with moisture etc. and has liquidresistance, and thus can sufficiently serve as a block against moistureetc. Further, the Yb layer is in direct contact with the entire surfaceof the organic light-emitting layers 17, and thus can exhibit highelectron injection properties.

The intermediate layer 18 in this case has a film thickness preferablyfrom 0.1 nm to 10 nm. This is because the single Yb layer having a filmthickness smaller than 0.1 nm might exhibit insufficient properties ofblocking moisture etc. and insufficient electron injection properties,while the single Yb layer having a film thickness larger than 10 nmcauses a problem in light-transmissivity and thus might exhibit adeteriorated luminous efficiency.

(D) The stability of Yb is high as described above. Accordingly, theintermediate layer 18 does not need to be provided and the secondfunctional layer 19 may include a single Yb layer such as illustrated inFIG. 18. It is considered that this causes the entire surface of Ybatoms to contact the counter electrode 20 and the organic light-emittinglayers 17, thereby increasing the stability of the electron injectionproperties.

The second functional layer 19 in this case has a film thicknesspreferably from 0.1 nm to 10 nm. This is because the single Yb layerhaving a film thickness smaller than 0.1 nm might exhibit insufficientproperties of blocking moisture etc. and insufficient electron injectionproperties, while the single Yb layer having a film thickness largerthan 10 nm causes a problem in light-transmissivity and thus mightexhibit a deteriorated luminous efficiency.

According to the present modification, the intermediate layer 18 can beomitted and thus the manufacturing process can be simplified.

(E) Also, the intermediate layer 18 does not need to be provided and thesecond functional layer 19 may include a mixture of NaF and Yb asillustrated in FIG. 19.

This second functional layer 19 is formed by for example co-depositionof NaF and Yb on the organic light-emitting layers 17.

With this structure, the second functional layer 19 itself has theelectron injection properties exhibited by Yb and the properties ofblocking moisture etc. which are the inherent function of theintermediate layer 18, and atoms of NaF and Yb are mixed togetherdispersedly in one layer, thereby achieving effects as follows.

Specifically, in the case where the second functional layer 19 (singleYb layer) is layered on the intermediate layer 18 (NaF) such asillustrated in FIG. 16, a reduction action of NaF by Yb exerts on only acontact part of the intermediate layer 18 which is in contact with thesecond functional layer 19. Accordingly, an increase in film thicknessof the intermediate layer 18 further promotes an increase in drivingvoltage. Thus, the purpose of improving the luminous efficiency might beinsufficiently achieved.

According to the present modification, however, since the single secondfunctional layer 19 includes NaF and Yb which are mixed together byco-deposition, reduction of NaF by Yb exerts on even an inner part ofthe layer. Accordingly, even when the film thickness of the secondfunctional layer 19 is increased to a certain extent, the electroninjection properties are unlikely to decrease, and thus the secondfunctional layer 19 serves a layer for adjusting an optical distance inan optical cavity structure. This eliminates the need to provide anyother special film thickness adjustment layer, thereby simplifying themanufacturing process to reduce the production cost, and alsoconstructing the optical cavity structure to seek an improvement inluminous efficiency.

In the present modification, a ratio (wt %) of a weight of Yb to a totalweight of NaF and Yb preferably ranges from larger than 73 wt % andsmaller than 100 wt %, and the film thickness of the second functionallayer 19 is preferably 10 nm or larger and smaller than 20 nm.

Further, in the present modification, a light-transmissive andelectrically-conductive film which includes metal oxide such as an IZOfilm and an ITO film is preferably formed on the second functional layer19 (however, such a film is not necessary to be newly provided in thecase where the counter electrode 20 originally includes thelight-transmissive and electrically-conductive film (IZO film) 20A suchas in the above embodiment).

In the present modification, the IZO film 23 is formed by sputtering.

Rare earth metal such as Yb typically has the following characteristics.When rare earth metal is oxidized, light-transmissivity is improved.Meanwhile, when single rare earth metal is oxidized, an oxide(passivity) is formed on only a surface of the single rare earth metal.Due to blocking by the oxide, which is formed densely on the rare earthmetal, Yb atoms in a further inner part of a layer is not oxidized.According to the present modification, however, since NaF and Yb areco-deposited and Yb atoms and NaF molecules are dispersedly present as amixture, the Yb atoms (Yb clusters) have gaps therebetween. SputteringIZO on the mixture, not only the Yb atoms on the surface are oxidized,but also IZO intrudes through the gaps between the Yb atoms and thus theYb atoms in the inside are successively oxidized. This helps tooxidization of even Yb atoms which are present at a significantly depthin the film thickness direction, thereby remarkably improving atransmittance.

(2) Other Modifications of Layered Structure of Organic EL Elements

In at least one embodiment, the first functional layers 22 each includetwo layers, namely, the hole injection layer 15 and the hole transportlayer 16. However, the present disclosure is not limited to this. Thefirst functional layer 22 may include either one of the hole injectionlayer 15 and the hole transport layer 16, or may be a hole injectiontransport layer including a material having characteristics of both thehole injection layers 15 and the hole transport layers 16.

Also, an electron injection layer may be separately added between thesecond functional layer 19 and the counter electrode 20.

Further, instead of the CF substrate 30, a polarizing filter substratemay be provided so as to improve antiglare properties.

(3) Modification of Bank and Pixel Partition Layer Forming Process

In at least one embodiment, the banks 14 and the pixel partition layers141 are formed in separate processes. However, the present disclosure isnot limited to this. The banks 14 and the pixel partition layers 141 maybe simultaneously formed by using a halftone mask, as follows.

First, the bank material layer 140 is formed by applying a resinmaterial by a wet process such as die coating onto the interlayerinsulating layer 12, on which the pixel electrodes 13 and the pixelpartition layers 141 are formed (see FIG. 10C).

It is preferable that for example, by for example vacuum drying andlow-temperature heating at an approximate temperature of 60° C. to 120°C. (pre-baking) after application, an unnecessary solvent is removed,and also the bank material layer is fixed onto the interlayer insulatinglayer 12.

Next, exposure is performed on the bank material layer 140 via aphotomask (not illustrated).

For example, in the case where the bank material layer 140 has positivephotosensitivity, parts of the bank material layer 140 to remain areshielded against light, and exposure is performed on parts of the bankmaterial layer 140 to be removed.

Since the pixel partition layers 141 have a smaller film thickness thanthe banks 14, half-exposure needs to be performed on parts of the bankmaterial layer 140 which are to remain as the pixel partition layers141.

For this reason, as a photomask for use in an exposure process, ahalftone mask having the following parts is used: light-shielding partswhich are provided in positions corresponding to the banks 14 andcompletely shield against light; light-semitransmissive parts which areprovided in positions corresponding to the pixel partition layers 141;and light-transmissive parts which are provided in positionscorresponding to exposed parts of the pixel electrodes 13 other than thebanks 14 and the pixel partition layers 141.

Transmittancy of the light-semitransmissive parts is determined suchthat exposure for a predefined period makes the bank material layer 140on the pixel electrodes 13 to be fully exposed and makes parts of thebank material layer 140 as the pixel partition layers 141 to remainunexposed by a height thereof.

Next, developing is performed, and the exposed parts of the bankmaterial layer 140 are removed. Thus, the banks 14 and the pixelpartition layers 141 which have a smaller film thickness than the banks14 are formed. Specific examples of developing methods include a methodof immersing the entire substrate 11 in a developer such as an organicsolvent and an alkaline solution which dissolves portions of the bankmaterial layer 140 which have been exposed to light, and then rinsingthe substrate 11 by a rinse solution such as pure water. Then, the bankmaterial layer 140 is baked at a predefined temperature.

As described above, the use of a halftone mask helps to form, on theinterlayer insulating layer 12, the banks 14 extending in the Ydirection and the pixel partition layers 141 extending in the Xdirection by the same process, thereby reducing the number of processesaccordingly. This contributes to cost reduction of organic EL displaypanel manufacturing.

(4) Modification for Banks Having Multi-Layer Structure

As described above, in the case where the first functional layers 22,the organic light-emitting layers 17, and the like are formed forconstructing an optical cavity structure by a printing method such thatthese layers each have a different film thickness between the lightemission colors, these layers sometimes have film shapes (especially,profiles of the surfaces in the cross-sections) slightly differingdepending on an ink application amount.

Typically, when an ink is dropped in the openings 14 a (see FIG. 3)between the adjacent banks 14, liquid surfaces of parts (pinning) of theink which are in contact with the banks 14 are higher than liquidsurfaces of central parts of the ink in the openings 14 a. After dryingthe ink in this state as it is, a thickness of parts near the banks 14tends to be larger than a thickness of the central parts. In particular,due to the organic light-emitting layers having a higher electricalresistivity than other organic functional layers, an electric currentmight concentrate in the central parts having a smaller film thicknessto shorten the operating life of the light-emitting elements, and thefilm shape is not stable and thus constructing an optical cavitystructure is difficult.

According to the present modification, in view of this problem, thebanks 14 have a multi-layer structure so as to uniformize a film shapeof organic layers formed by a printing method.

FIG. 20 is a schematic cross-section diagram illustrating a structure ofa display panel 10′ pertaining to the present modification. In thefigure, numerical reference the same as in FIG. 4 represent structureelements the same as in FIG. 4, and accordingly description thereof isomitted. In addition, a substrate 11, a CF substrate 30, and so on arenot illustrated.

As illustrated in FIG. 20, the display panel 10′ includes light-emittingparts each of which is formed by layering a pixel electrode 13, a holeinjection transport layer 24, an organic light-emitting layer 17 (17(R),17(G), or 17(B)), an intermediate layer 18, a second functional layer19, a counter electrode 20, and a sealing layer 21 in this order. Thehole injection transport layer 24 and the organic light-emitting layer17 are formed by a printing method.

In addition, in the present modification, banks 440 have a multi-layerstructure including a first layer 441 to an eighth layer 448. Amongthese layers, the odd ordinal numbered layers 441, 443, 445, and 447include a material having a higher liquid repellency than the evenordinal numbered layers 442, 444, 446, and 448 include.

With this structure, for example when an ink of amount necessary to forman applied film having a target film thickness as the hole injectiontransport layer 24 in a subpixel 100B is dropped, parts (pinningposition) of liquid surfaces of the ink which are in contact with thebanks 440 are not in contact with the seventh layer 447, which has ahigher liquid repellency, and remain at a border between the seventhlayer 447 and the eighth layer 448, which has a lower liquid repellency.Accordingly, adjustment of the ink amount to be dropped allows to obtainthe hole injection transport layer 24 which has a surface whose heightis substantially equal to a height of the border between the seventhlayer 447 and the eighth layer 448 and has a uniform film thickness.

To increase the film thickness of the hole injection transport layer 24such as in a subpixel 100G, pining is positioned at a border between thefifth layer 445 and the sixth layer 446. Accordingly, by adjusting theink amount so as to reach the height of the border, it is possible toobtain the hole injection transport layer 24 in the subpixel 100G with asubstantially uniform film thickness which is larger than the filmthickness of the hole injection transport layer 24 in the subpixel 100Bby the total film thickness of the sixth layer 446 and the seventh layer447 in the subpixel 100B.

Such a method helps to form the hole injection transport layers 24 andthe organic light-emitting layers 17 having substantially uniform filmthicknesses corresponding to the light emission colors.

Note that FIG. 20 is just a schematic diagram. In practice, filmthicknesses of layers for effectively obtaining an optical cavitystructure are determined by design, and the number of layers to beincluded in the banks 440 and film thicknesses of the layers are set inaccordance with the determined film thicknesses. This achieves a displaypanel having a further excellent luminous efficiency.

(5) According to the display panel 10 pertaining to at least oneembodiment, as illustrated in FIG. 2, the pixel partition layers 141extend in the long-axis X direction of the display panel 10 and thebanks 14 extend in the short-axis Y direction of the display panel 10.However, the present disclosure is not limited to this. The extendingdirections of the pixel partition layers 141 and the banks 14 may bereversed. Alternatively, the extending directions of the pixel partitionlayers 141 and the banks 14 may be directions independent of the shapeof the display panel 10.

Also, according to the display panel 10 pertaining to at least oneembodiment, the image display surface has a rectangular shape as anexample. However, the shape of the image display surface is not limitedto this and may be modified as appropriate.

Further, according to the display panel 10 pertaining to at least oneembodiment, the pixel electrodes 13 are rectangular plate-like members.However, the present disclosure is not limited to this.

Moreover, in at least one embodiment, the description has been providedon an organic EL display panel employing the line bank structure.However, the present disclosure is not limited to this and may be anorganic EL display panel employing a so-called pixel bank structure inwhich all sides of each subpixel are surrounded by banks.

However, when the line bank structure is employed, an effect of adoptingYb having liquid resistance as a metal dopant of the second functionallayer 19 is exhibited further greatly, compared with the pixel bankstructure. This is because according to the line bank structure, thelight-emitting layers are formed even on the pixel partition layers 141and thus a larger amount of ink is dropped and a larger amount ofmoisture etc. remains after drying, compared with the pixel bankstructure.

Also, the organic EL elements (light-emitting parts) only need to betwo-dimensionally arranged above the substrate across the main surfaceof the substrate, and do not necessarily need to be arranged exactly ina matrix. For example, the subpixels each having a regular hexagonalshape in plan view may be arranged in a honeycomb structure.

(6) In at least one embodiment, the hole injection layers 15, the holetransport layers 16, and the organic light-emitting layers 17 are allformed by a printing method (application method) such that the thicknessdiffers between the R, G, and B colors. However, the present disclosureis not limited to this. Only one layer among these layers may be anapplied film which is formed by a printing method, in accordance with atarget optical cavity structure. Note that whether a certain layer in afinished product of the display panel 10 is an applied film or not canbe easily determined by detecting moisture or solvent remaining in thelayer.

(7) In the display panel 10 pertaining to at least one embodiment, thesubpixels 100R, 100G, and 100B, which emit light of the R, G, and Bcolors respectively, are arranged. However, the light emission colors ofthe subpixels are not limited to these and may be for example fourcolors including yellow (Y) color in addition to the R, G, and B colors.Also, the number of subpixels per color arranged in one pixel P is notlimited to one, and may be plural. Further, the arrangement order of thesubpixels in each pixel P is not limited to the red, green, and bluesuch as illustrated in FIG. 2, and the subpixels may be reordered amongthese colors.

(8) Adoption to Flexible Display Panel

A display panel achieves flexibility and sealing properties by includingthe base material 111 of the substrate 11 formed from a resin film andincluding the sealing layer 21 formed from two-layered thin filmsincluding an inorganic material which sandwich a resin material (organicfilm) therebetween. In such a display panel, adoption of Yb as a metaldopant of the second functional layer 19 such as in the above embodimentincreases water resistance. Thus, durability of the sealing layer can besufficiently achieved simply by layering one inorganic film and oneorganic film, thereby simplifying a sealing structure in a flexibledisplay panel.

(9) Further, in at least one embodiment, the display panel 10 employsthe active matrix system. However, the present disclosure is not limitedto this, and a passive matrix system may be employed.

Moreover, the present disclosure is applicable not only to organic ELdisplay panels of the top-emission type but also to organic EL displaypanels of a bottom-emission type.

In the case of the bottom-emission type, the counter electrode 20 is alight-reflective anode and the pixel electrodes 13 are cathodesincluding a light-transmissive material (including alight-semitransmissive material). In accordance with this, the layeringorder of other layers including the first functional layers 22, theintermediate layer 18, and the second functional layer 19 is differentfrom that in the top-emission type.

Further, the base material 111 and the interlayer insulating layer 12include a light-transmissive material. The drive circuits including TFTsin the TFT layer 112 are formed at positions overlapping the banks 14and the pixel partition layers 141 in plan view so as not to shieldagainst emitted light. Moreover, the CF substrate 30 may be attachedonto the substrate 11 side. Alternatively, the CF substrate 30 itselfmay serves as the base material 111 of the substrate 11.

The present modification is generalized as follows. (a) One of a firstelectrode and a second electrode has light-reflectivity and the otherhas light-transmissivity; and thickness of a light-emitting layer and/orthickness of a functional layer disposed between the light-reflectiveelectrode and the light-emitting layer differs between the firstlight-emitting part and the second light-emitting part which differs inlight emission color from each other.

(b) The functional layer, which is disposed between thelight-transmissive electrode and the light-emitting layer, includesytterbium.

(c) The light-emitting layer and the functional layer, which is disposedbetween the light-emitting layer and the light-reflective electrode,include an applied film.

By satisfying the above requirements, the effects by the presentdisclosure can be achieved in common irrespective of the top-emissiontype or the bottom-emission type.

(10) In at least one embodiment, the structure is described in which onepixel includes three light-emitting parts (organic EL elements) whichemit light of R, G, or B light emission color. However, the presentdisclosure is not limited to this, and one pixel may include two or fouror more light-emitting parts in some cases.

Also, light-emitting parts included in one pixel do not necessarilydiffer in light emission color from each other. To achieve the effectsby the present disclosure, it is only necessary that at least one oflight-emitting parts included in one pixel differs in light emissioncolor from any other of the light-emitting parts and that at least oneof a light-emitting layer and a first functional layer included in theat least one light-emitting part differs in film thickness from that inthe any other light-emitting part for the purpose of construction of anoptical cavity structure.

(11) Description has been provided above of a method of manufacturing anorganic EL display panel in which organic EL light-emitting layers areused. However, in addition to such organic EL display panels, displaypanels such as quantum dot display panels in which QLEDs are used aslight-emitting layers (see, for example, Japanese Patent ApplicationPublication No. 2010-199067) have a structure similar to organic ELdisplay panels in which light-emitting layers and other functionallayers are disposed between pixel electrodes and a counter electrode,although structures and types of the light-emitting layers aredifferent. Accordingly, the present disclosure is applicable toformation of such display panels when an application method is used forforming the light-emitting layers and other functional layers.

<<Supplement>>

Description has been provided above of display panels and display panelmanufacturing methods pertaining to the present disclosure based onembodiments and modifications, but the present disclosure is not limitedto the embodiments and modifications described above.

Although one or more embodiments pertaining to the present disclosurehave been fully described by way of examples with reference to theaccompanying drawings, it is to be noted that various changes andmodifications will be apparent to those skilled in the art. Therefore,unless such changes and modifications depart from the scope of thepresent disclosure, they should be construed as being included therein.

1. A display panel in which pixels each including light-emitting partsare two-dimensionally arranged across a main surface of a substrate,wherein the light-emitting parts each comprise: a first electrode thatis light-reflective; a first functional layer that is disposed above thefirst electrode; a light-emitting layer that is disposed above the firstfunctional layer; a second functional layer that is disposed above thelight-emitting layer and includes ytterbium; and a second electrode thatis disposed above the second functional layer and is light-transmissive,at least one of the light-emitting layer and the first functional layeris an applied film, with respect to each of the pixels, at least one ofthe light-emitting parts differs from any other of the light-emittingparts in terms of light emission color, and the at least onelight-emitting part differs from the any other of the light-emittingparts in terms of film thickness of at least one of the light-emittinglayer and the first functional layer.
 2. The display panel of claim 1,wherein the light-emitting parts each further comprise an intermediatelayer that is disposed between the light-emitting layer and the secondfunctional layer, and includes a fluoride of a metal selected fromalkali metals or alkaline earth metals.
 3. The display panel of claim 1,wherein the light-emitting parts each further comprise an intermediatelayer that is disposed between the light-emitting layer and the secondfunctional layer, and is a single ytterbium layer.
 4. The display panelof claim 1, wherein the second functional layer includes an organicmaterial doped with ytterbium.
 5. The display panel of claim 4, whereina doping concentration of the ytterbium ranges from 3 wt % to 60 wt %.6. The display panel of claim 1, wherein the second functional layer isa single ytterbium layer.
 7. The display panel of claim 1, wherein thesecond functional layer includes ytterbium and a fluoride of a metalselected from alkali metals or alkaline earth metals.
 8. The displaypanel of claim 7, wherein the light-emitting parts each further comprisea light-transmissive and electrically-conductive film that is disposedbetween the second functional layer and the second electrode so as to bein contact with the second functional layer, and includes inorganicoxide.
 9. The display panel of claim 8, wherein the light-transmissiveand electrically-conductive film is an indium tin oxide (ITO) film or anindium zinc oxide (IZO) film.
 10. The display panel of claim 1, whereinthe first electrode is a light-reflective anode, and the secondelectrode is a light-semitransmissive cathode.
 11. A method ofmanufacturing a display panel in which pixels each includinglight-emitting parts are two-dimensionally arranged across a mainsurface of a substrate, the method comprising, for each of thelight-emitting parts: forming a first electrode above the substrate;forming a first functional layer above the first electrode; forming alight-emitting layer above the first functional layer; forming a secondfunctional layer above the light-emitting layer; and forming a secondelectrode above the second functional layer, wherein one of the firstelectrode and the second electrode is a light-reflective electrode, andthe other is a light-transmissive electrode, out of the first functionallayer and the second functional layer, one functional layer that isdisposed between the light-reflective electrode and the light-emittinglayer includes ytterbium, at least one of the light-emitting layer andthe other functional layer out of the first functional layer and thesecond functional layer is formed by an application method, with respectto each of the pixels, at least one of the light-emitting parts differsfrom any other of the light-emitting parts in terms of light emissioncolor, and the at least one light-emitting part differs from the anyother of the light-emitting parts in terms of film thickness of at leastone of the light-emitting layer and the other functional layer out ofthe first functional layer and the second functional layer.